Telecommunication advances are permitting richer communication experiences, including telephony experiences. A known telephony features is Multi-level Precedence and Preemption (MLPP). MLPP is a specification used for military Department of Defence (DOD) networks and is required by DOD. The specification is defined according to the Integrated Services Digital Network (ISDN) under a Defence Switched Network (DSN) specification which uses information element 619. With MLPP, one can declare an emergency at different levels. It allows preemption of people using certain resources or people. For example, if a general wants to connect to a lieutenant, and the lieutenant is already on the phone, the general can barge in and preempt the lieutenant's ongoing call. The lieutenant hears a tone then the general is connected. As another example, a politician can invoke an MLPP override to get to an emergency team head during a disaster. In general, MLPP allows high priority people to get the resources they need.
MLPP has not been more broadly implemented in the traditional public switched telephone network (PSTN) due to the potential for abuse through irresponsible or malicious actions. An example of a variation of MLPP is disclosed in EP 1560456B1, which discloses a mobile switching center that performs a barge-in that allows a first user to communicate with a second user of a mobile communication device that is engaged in a preexisting active call. However, EP 1560456B1 still leaves certain potential for irresponsible or malicious actions. The application of MLPP in a private branch exchange (“PBX”) is prone to similar abuses.